U.S. Pat. No. 6,624,522 (IR-1830) shows a semiconductor package known by the trademark Direct FET, a trademark of the International Rectifier Corporation, in which semiconductor die are contained within a conductive clip or flat cup with one surface of the die connected to the interior surface of the clip and with the opposite surface and its electrodes generally coplanar with the bottom of the clip so that it can be conductively fastened to a support circuit board. The clip itself may be a contact for electrodes of the die connected to the interior of the clip, with all device electrodes being available for connection to the contact patterns of the flat circuit board.
It is frequently desirable to copack plural die in such a package, for example, to form a half-bridge topology in a single package for such applications as a synchronous buck converter, lighting controls, class D audio circuits and the like.
FIG. 1 shows a typical half bridge circuit consisting of series connected power MOSFETs 20 and 21 having gates G1 and G2 respectively. The series circuit is connected to upper terminal V(+) and lower terminal V(−), which may be ground potential, and an output central terminal “out”.
It would be very desirable to house MOSFETs 20 and 21 in a single common housing, schematically shown by dotted rectangle 22, with the 5 terminals accessible for easy connection to the terminals of a flat circuit board as by soldering or conductive cements, or the like. The circuit board may be of any desired material, such as IMS, DBC, FR4 or the like. The shape of the board can be any shape desired.
By copacking the two MOSFETs 20 and 21 (or any other circuit component) customer part count is reduced and parasitic inductance and resistance is reduced.
The present Direct FET package format only allows for copackaged die with a common drain at the node between the die. Thus it is not suitable for a half bridge circuit such as that of FIG. 1 in which the source of FET 20 is connected to the drain of FET 21. Thus, added connection tabs are needed for this purpose as shown in U.S. Pat. No. 6,677,669 (IR-2107) for plural MOSFETs in a Direct FET package.
Consequently, copacks without a common drain have required wire bonded packages such as the SO-8, or the 5 lead TO-220 packages. See for example, U.S. Pat. No. 7,095,099 (IR-2613). These, however, will have a higher inductance and higher RDSON than a copack in a Direct FET package and have poorer thermal performance than that of the Direct FET packages.
It is very desirable to be able to employ the Direct FET type package for copacked FETs without a common drain connection and without the need for wire bonds or special clips, or the formation of a patterned insulation layer inside the can or clip to insulate at least one of the FET terminals from the conductive clip.